1. Field of the Invention
This invention relates to a control system for a four-wheel-steered vehicle provided with a traction control system.
2. Description of the Prior Art
Recently there has been put into practice a four-wheel-steered vehicle in which both the front and rear wheels are turned when the steering wheel is turned. In such a four-wheel-steered vehicle, the rear wheels are turned according to predetermined rear-wheel turning characteristics which determines the rear wheel turning angle ratio (the ratio of the rear wheel turning angle to the front wheel turning angle). Generally, the rear wheels are turned in the same direction as that of the front wheels when the vehicle speed is relatively high and in a direction opposite to that of the front wheels when the vehicle speed is relatively low. In this specification, that the rear wheels are turned in the same direction as that of the front wheels will be expressed as "the rear wheels are turned in the same phase", and that the rear wheels are turned in a direction opposite to that of the front wheels is expressed as "the rear wheels are turned in the reverse phase". When the rear wheel turning angle ratio is positive, the rear wheels are turned in the same phase and when the rear wheel turning angle ratio is negative, the rear wheels are turned in the reverse phase.
Further, there has been known a traction control system which controls the driving force of the driving wheels when the slip ratio of the driving wheels with respect to the road surface exceeds a preset slip ratio. (See Japanese Unexamined Utility Model Publication No. 60(1985)-60356, for instance.)
Recently there has been proposed a total vehicle control system which controls the four-wheel steering system and the traction control system in combination with each other in order to improve total balance of the vehicle.
Such a total vehicle control system can be better used when it is arranged so that when a failure occurs in one of the control systems, the failure can be compensated for by properly controlling the other control system.